I'd like to know how I would use Quick Masks in Photoshop (CS5) to blur all layers below the masked layer.
Maybe I am reading it wrong but what your wanting to do doesn't make sense... Quick Mask creates a channel and that channel is transformed into a marching ants selection after you exit Quick Mask mode.
There is no Quick Mask Layer and I am also pretty sure you cannot create a layer that blurs other layers.
What you can do is create a layer composed of the other layers and then blur that layer... Ctrl+Alt+Shift+E merges all layers into a new layer leaving the originals untouched.
You can convert a group of layers into a Smart Object, using "Convert for Smart Filters" under the Filter menu. Then, you can use filters like Blur, with a mask, and you will affect all layers within that Smart Object.
This is superior to merging the layers because you can still edit or extract the individual layers. It is still not as convenient as it might be, because you must open the Smart Object any time you want to make changes to these layers.